It would be worth more than that.
It’s per user revenue is low and can be increased to $20 as author notes.
Today’s market values growth over everything and since they are profitable they will get a steep multiple.
Markets are irrational and trade on momentum.
The valuation provided is more of the floor than what it would trade based on growth expectations and general excitement.
Unlike FB which has competition from Twitter and Snapchat and would be suffering had it not acquired Instagram, YouTube itself has no direct competition in its space.
More likely it would trade at $250-350b
Either way it along with Instagram are the two best acquisitions in modern tech history.